src/d2m/actions/remove-member.js

@@ -19,7 +19,18 @@ async function removeMember(userID, guildID) {
 		}
 	})()
 	for (const m of membership) {
-		await api.leaveRoom(m.room_id, m.mxid)
+		try {
+			await api.leaveRoom(m.room_id, m.mxid)
+		} catch (e) {
+			if (String(e).includes("not in room")) {
+				// no further action needed
+			} else {
+				throw e
+			}
+		}
+		// Update cache to say that the member isn't in the room any more
+		// You'd think this would happen automatically when the leave event arrives at Matrix's event dispatcher, but that isn't 100% reliable.
+		db.prepare("DELETE FROM sim_member WHERE room_id = ? AND mxid = ?").run(m.room_id, m.mxid)
 	}
 }
 

src/d2m/event-dispatcher.js

@@ -125,6 +125,7 @@ module.exports = {
 			// Send in order
 			for (let i = Math.min(messages.length, latestBridgedMessageIndex)-1; i >= 0; i--) {
 				const message = messages[i]
+				if (message.type === DiscordTypes.MessageType.UserJoin) continue // since join announcements don't become events, it would be a repetition to act on them during backfill
 
 				if (!members.has(message.author.id)) members.set(message.author.id, await client.snow.guild.getGuildMember(guild.id, message.author.id).catch(() => undefined))
 				await module.exports.MESSAGE_CREATE(client, {